In the field of washing and bleaching fabrics, the use of a combination of a hydrogen peroxide precursor (perborate tetrahydrate and percarbonate) and an O-acyl activator (e.g. pentaacetylglucose) and an N-acyl donor (e.g. tetraacetylenediamine) in the same or in different compositions is known. Once dispersed in water, these components react with each other to form the peroxyacid anion. This reaction occurs in a strictly aqueous environment and at an invariably alkaline pH (pH>9). Peracid anions are instantly released upon mixing the two components with water that can have been heated to a greater or a lesser extent. Peroxyacid stability in this environment is limited to the point that the solution cannot be reused for an effective bleaching and disinfection process.
In these formulations, the activator and the peroxide source do not react with each other during storage, and are both stable under the usual storage conditions (temperature not higher than 40° C.). Several proposals have already been suggested (see e.g. WO-A-9213798) according to which, the N-acyl and the O-acyl donors are covered with or aggregated by solid organic acids such as citric, lactic and glycolic acid, so that a longer storage duration is obtained. Other proposals aim at using acylated citrate esters (see WO-A-93167), or N-acyl lactams and other acyl donors. Independently from the use and the activating species, all the above prior art proposals have the following features in common:                they react in an alkaline environment;        they form peroxyacid anions in situ;        the dilute solution is immediately used as a bleach and/or disinfectant;        limited stability of the solutions with time, owing to the degradation of hydrogen peroxide being promoted in an alkaline environment (with consequent release of oxygen), which, in turn, results in the reaction equilibrium of the peracetic acid reaction being shifted back leftwards, yielding to a decrease in its concentration (see the reaction diagram shown below):        

Conversely, an acidic environment clearly promotes greater stability with time of both the hydrogen peroxide, and the peracid. All commercially available concentrated and diluted solutions based on hydrogen peroxide and peroxyacids have an acidic pH for this reason, for the very reason of preserving their characteristics for the longest possible time in standard storage conditions.
It is also well-known to the skilled person in the art that organic peroxyacids can be used as strong oxidizing agents for a wide variety of oxidation reactions that occur in up to (quantitatively) high yields. In many reactions for preparing these peroxyacids (see in particular “Organic Peroxides” volume 1, Ed. D. Swern, Wiley Interscience (1970) 313–335) the carboxylic acid or anhydride, or their most reactive acyl chloride or aldehyde are used as a starting material for a perhydrolysis reaction caused by hydrogen peroxide.
GB-A-931,119 describes for instance a process for producing the peroxyacid by means of the hydrogen peroxide reaction with an ester of the organic carboxylic acid, in the absence of water and in the presence of a minimum quantity of a strong inorganic acid that acts as a catalyst. This process requires that the hydrogen peroxide be dissolved in liquid ester, that water be removed and that the acid catalyst be added only upon complete removal of water.
Moreover, anhydrous processes for producing aliphatic or aromatic percarboxylic acids have been proposed. DE-3638552 discloses an innovative apparatus for the production of percarboxylic acids on an industrial scale. All these methods are special processes useful for a synthesis on a laboratory or industrial scale, but certainly not for use in the health-care, household environments or in general. Some starting reagents are in fact very dangerous, and thus they can be handled only by specialized personnel each equipped with suitable protective clothing. Other starting materials, such as acetic anhydride, are sensitive to water because of their high reactivity, and thus need to be stored under special conditions.
With reference to the detergent formulations used for bleaching fabrics, Croud et al., (WO 94/18297) have proposed a system having the same advantages as those of bleaching combinations, but where the reaction between precursor (peroxide source) and activator and/or the subsequent oxidation step is carried out under acidic conditions and at relatively low concentrations. The reaction is carried out in a typically aqueous environment at a pH lower than 6.5. Moreover, in the several Examples set forth in WO94/18297 formulations are disclosed, in which both active components (peroxide source and activator) are in solid form under given storage conditions as a single composition or as separate compositions, and thus need a third liquid component (water) so that their reaction can take place. In the same document, various concentrations of hydrogen peroxide are provided up to a maximum of 60% w/w. Even the operating temperature can vary up to a maximum of 95° C. In the formulation, there is provided a component releasing an acidic species, or suitable for reacting with a by-product of the perhydrolysis reaction for decreasing pH and maintaining the solution at a pH lower than 7. Such a component can be present as a single composition together with the activator, and be a polyol, an organic polycarboxylic acid, boric acid and sodium di-hydrogen phosphate. The formulation can also comprise a surfactant. The presence of the last component is to be ruled out in washing operations in washing-machines involving shaking, since an excessive amount of foam would be produced, and thus the washing machine would discontinue its operation.
In WO 96/18297 a typically solid biocidal composition is disclosed, which contains a peracetic anion generating system mixed with a stabilizing organic acid (citric acid, succinic acid) selected for its ability, when this composition is added to an aqueous solution at suitable concentrations, to control peracetic ion release into such aqueous solution with time. The relative ratios between the components of the generating system, on the one hand, and the stabilizing organic acid, on the other, are adjusted so that the concentration of the generated peracetic acid is higher than a concentration threshold above which it can induce a biocidal effect for a predetermined time length of action, e.g. longer than 24 hours.
The composition disclosed by the above prior art document is in solid form and substantially based on three components:                H2O2 and/or generator of peroxides, e.g. persalts, such as perborates, persulphates, percarbonates,        products whose properties as activators of O-acyl and/or N-acyl donating bleaching compositions of the TAED type (tetraacetylethyldiamine, acetylated sugars or other compounds of this type disclosed in the references of the state of the art);        organic polycarboxylic acid, such as citric acid and succinic acid.        
Such a solution, once dispersed in water, yields peracetic ions as a disinfecting active principle with a long-lasting action.
U.S. Pat. No. 5,350,563 (Kralovic et al.) discloses a powdered formulation in which, regardless of whether they be stored in two or three compartments, to react with one another, the various components in the solid state are mixed in water, that makes up a further component. In Kralovic's method a (solid) perborate stored in one compartment is used as an active oxygen source, whereas a (solid) TAED acetylating agent is stored in the other. The compartments can also contain compositions in the solid state, such as a buffer system for controlling pH, corrosion-preventing materials, surfactants, sequestring agents and the like. However, the different components must always be dissolved in a liquid solvent and according to a very precise addition sequence, owing to higher or lesser susceptibility of the N-acyl and/or O-acyl donors to inactivation triggered by hydrolysis. Kralovic's powdered mixture was actually already known to the skilled persons in the art since it had already been widely used as a bleach for fabrics. Kralovic disclosed that the use of fast-rate and slow rate acetylating agents in a 1 to 1 molar ratio in powdered mixture makes it possible to obtain a solution with a more stable peracetic acid concentration of 2000 ppm. The fast-rate acetylating agent, that] in the above cited Examples corresponds to TAED (tetraacetyldiamine) is so defined since, the other conditions (pH and solution temperature) being equal, it undergoes an attack by peroxide ions at a fast rate.
The slow rate acetylating agent (acetyl salicilic acid in the above cited Examples) on the other hand undergoes a slower rate and delayed perhydrolysis, and thus it contributes in keeping the concentration of the initially formed peracetic acid stable with time in the solution. This too, like the previous composition disclosed by WO 96/18297, is a composition that, once dispersed in water, yields to a biocidal solution based on peracetic acid that is stable with time.
In U.S. Pat. No. 4,900,721 (Bansemir et al.) the synergistic biocidal effect obtained by combining hydrogen peroxide or peracids with alcohols is disclosed.
In other words, the association of alcohols, on the one side, and organic peroxyacids and hydrogen peroxide, on the other, proposed by Bansemir, has a biocidal effect that is too limited to meet the requirements of the high level disinfection typical of the health-care field.
The preparation of peracetic acid in situ by reaction of hydrogen peroxide with peracetic anhydride and/or acetic acid in the presence of an inorganic acid catalyst is used in agriculture for carrying out controlled disinfection of hydroponic seedings as disclosed in EP-0 361 955. In fact, such method makes it possible to significantly reduce the risks associated with shipping and subsequent handling of concentrated peracetic-acid-based solutions. Such solutions are in fact corrosive and combustive, and thus, when preparing diluted solutions starting from said solutions, strict handling precautions must be adopted.
EP-0 12 781 discloses the use of O-acyl donor compounds and organic acids for the production of their respective peroxyacids by a catalyzed acid and base perhydrolysis reaction. Such compositions containing these activators are used for cleaning, bleaching and disinfecting fabrics.
U.S. Pat. No. 5,279,735 discloses dyes that are stable to oxidation and thus can be used to dye organic peroxyacid-based solutions over a predetermined period of time.
EP-0 953 283 (Farmec) describes a two-component system for preparing a peracetic acid based hydroalcoholic solution in situ. Such a system is, however, affected by some limitations substantially due to the following:
the system is not always adequately stable with time and provides for an N-acetyl and O-acetyl donor being dissolved in an aqueous environment, the donor undergoing degradation, particularly at relatively high temperatures (such as those reached in summertime);
no buffer system is provided in the parent solution that is suitable for simultaneously obtaining an effective and fast activation and a biocidal activity over a prolonged period of time.